130 REPORT OF THE Xo. 55 



precise definition as* to temperature and length of time, pasteurization is found to 

 be a very elastic term.' Some, we found ran milk over coils for 30 to 40 seconds 

 .at a temperature of from 165 degrees to 185 degrees and called it pasteurization; 

 this is also known as "continuous" or "commercial" pasteurization. Others held 

 it for from 20 to 30 minutes at from 140 degrees to 157 degrees; this is known 

 as "scientific" pasteurization. Still others, like Chicago, have a sliding scale both 

 of time and temperature. Some few pasteurize after the milk has been placed in 

 bottles and thereby avoid absolutely the possibility of further contamination; others 

 pasteurize in open vats., over coils or in closed holding devices. 



The object of pasteurization is to kill the bacteria. But there are many kinds 

 of bacteria in milk and some are not so easily killed as others. On this point 

 hinges the question of the length of time required for effective pasteurization. 

 Moreover, the different kinds of bacteria have different influences. On this point 

 hinges the controversy over the wisdom of pasteurizing at all. When it is said 

 that a sample of milk contains one million bacteria per cc. (cubic centimetre), 

 which means a million infinitesimal germs in sixteen drops of milk, it must not 

 be supposed that they are all pathogenic or disease-producing. As a matter of 

 fact, it is probable that few are disease-producing, while a very large number are 

 lactic acid bacteria, which are not only harmless, but useful in that they are 

 Nature's check on the injurious bacteria. Thousands of people who do not know 

 the cause know that milk if kept a certain length of time the higher the tem- 

 perature the shorter the time will sour. Science explains that lactic acid bac- 

 teria are the cause. It is also known that milk spreads disease. Science explains 

 that certain pathogenic germs are the cause of tuberculosis, typhoid fever, scarlet 

 fever and diphtheria. They, however, are not killed as easily by pasteurization 

 as the lactic acid germs. 



Pasteurization has been in use in the 'larger dairies on this continent for at 

 least ten or twelve years. It finds 1 greater favour with the large dairy companies 

 than with the small. With few exceptions, the "continuous" process has been used 

 and the main object has been to destroy the lactic acid bacteria in order to pre- 

 vent souring. In large cities where milk had to be brought long distances and 

 where 24 to 36 hours elapsed before it reached the consumer, this was a material 

 commercial advantage. During recent years more attention has been paid to the 

 value of pasteurization as a means of preventing milk-borne diseases, and then 

 it was found that the existing system was all wrong. A continuous flow of milk 

 over a coil at a temperature of 160 degrees to 180 degrees killed the lactic acid 

 germs and prevented souring, but did not always kill the germs which, if present, 

 spread disease. Many eminent names might be quoted, but it is sufficient to say 

 that the weight of scientific testimony now agrees that nothing short of 140 degrees 

 for twenty minutes will assure absolute immunity from all disease germs, the tub- 

 ercle bacilli being the most resistent. Some say 140 degrees for thirty minutes or 

 157 degrees for twenty minutes. 



But what of milk after pasteurizing? If only the lactic acid germs are 

 destroyed, then the pathogenic, freed from germicidal restraint, proliferate more 

 rapidly and there is an increase in virulence. If both lactic acid and pathogenic 

 are destroyed, milk cannot be disease-producing without reinfection, but unless 

 the milk is carefully handled, it will in the course of time become putrid, owing 

 to the presence of spores. But the destruction of the bacteria gives' an evenness of 

 flavour specially valuable in butter-making. The other question is at to whether 

 pasteurization alters the taste or digestive quality of the milk. While there is con- 



